Customization geeks, here's a noteworthy app that will likely soothe the customization needs you didn't know you had.
Adapticons is an Android app that lets you customize the icons of the apps you have installed on your phone to a certain extent. For example, you can take a ton of shapes and plaster them as backgrounds for the icons. This way, you can easily create a circular icon out of an otherwise square app icon, or even go for the trendier squircle, hexagon, roundy, and other shapes. You can also select a color for the background or let the app select this one on its own. There's also the option to employ a long shadow effect which helps in creating a more dynamic and interesting look. Resizing the app icon relative to the background shape is also a feature of the app, which is great.
Another intriguing feature of Adapticons is that it allows you to select a new icon from a compatible icon pack you have installed on your phone and even change the overall color of that one for a more coherent and sleek look.
Once you're done, you can apply a single icon to the respective app, save it as a .PNG file, or create your own icon pack from a bunch of icons that can subsequently get imported within a compatible custom launcher, like the omnipotent Nova Launcher.
The app is free, but in order to utilize it's full potential you will have to unlock its premium version, which goes for a $1 as we speak.